Outgoing Health and Human Services Secretary Kathleen Sebelius, who announced her resignation earlier this month, said the numbers reflect “an unprecedented outreach and enrollment effort” involving state and local partners and “health navigators.”

The new report comes a day after the release of a Republican analysis indicating that only 67 percent of people who enrolled through the federal HealthCare.gov marketplace had paid their first month’s premium.

Enrollment in health plans is not complete until consumers make the initial premium payment.

Critics of the Affordable Care Act — or “Obamacare”, as some people call it — have questioned the administration’s enrollment figures. They say the numbers reported by the administration don’t reflect the number who completed the enrollment process by paying their first premium.

White House Spokesman Jay Carney on Thursday dismissed the GOP numbers, saying that people who signed up in the final weeks of open enrollment may not have even received a bill yet.

Health officials won’t have the number of paid enrollments until later this year, U.S. Health and Human Services Spokeswoman Julie Bataille said during an afternoon news conference.

The Affordable Care Act created federal and state marketplaces where consumers can shop for a health insurance plan. Open enrollment for most people ended March 31, although the administration allowed extra time for people who started the enrollment process but were unable to complete it by the deadline.

The Congressional Budget Office initially projected that 7 million people would sign up for health coverage in 2014. It later lowered its estimate to 6 million.

Following the dismal rollout of the HealthCare.gov website last October and computer problems affecting state exchanges, it seemed for many months that total enrollment would fall far short of those projections. But a last-minute surge in applications helped boost enrollment above the 8 million mark, a milestone cited by President Barack Obama at an April 17 press conference.

“This thing is working,” he said of the health-reform law, which is considered his signature domestic policy achievement.

The enrollment report released Thursday shows that 28 percent of people who selected a marketplace plan were young adults ages 18 to 34. Younger adults’ participation in the new health insurance plans is considered crucial because they tend to be healthy and less costly to cover. Their insurance premiums should help to offset the higher costs of medical treatment of older, sicker adults.

The new report also provides the first official breakdown of enrollment by race and ethnicity. Of people who chose to report their race or ethnicity on their application for coverage through the marketplaces, 16.7 percent were African American and 10.7 were Latino.

On Wednesday, the Republican-led House Energy and Commerce Committee reignited debate over the Obamacare enrollment figures, saying it had contacted every health insurer participating in the HealthCare.gov federal marketplace. The panel’s finding: just two-thirds of people who enrolled through HealthCare.gov had paid their initial premium.

HealthCare.gov is the portal that consumers in 34 states used to sign up for Obamacare. Sixteen states and the District of Columbia run their own exchanges.

The GOP data represent all 160 providers in the federal exchange, yielding “a snapshot of the true enrollment picture as of April 15, 2014,” the committee said.

Most Americans won’t have another chance to sign up for coverage through the exchanges until the next open enrollment period, which begins Nov. 15. Coverage purchased during that time won’t take effect until 2015.